Venous and Lymphatic Disorders

Question 1

Peripheral vascular disease denotes disorders of peripheral vessels including ………………………………(5).

Answer 1

Peripheral vascular disease denotes disorders of peripheral vessels including arteries, arterioles, veins, venules, and lymphatics.

Question 2

Vascular lesions may result from ………. vascular pathology or occur ………………… to conditions originating in …………… tissues or organ systems.
Resultant conditions may remain asymptomatic with little or no effect on morbidity and mortality or progress to become life threatening.

Answer 2

Vascular lesions may result from primary vascular pathology or occur secondary to conditions originating in unrelated tissues or organ systems. Resultant conditions may remain asymptomatic with little or no effect on morbidity and mortality or progress to become life threatening.

Question 3

TECHNIQUES USED TO EVALUATE VENOUS AND LYMPHATIC DISEASE

Angiography

Angiography is the gold standard for evaluating peripheral vascular diseases due to its ability to characterize and visualize normal and abnormal vascular anatomy.[1] Diagnostic outcome requires careful attention to three important elements: selection of radiopaque contrast agent, technique for vascular delivery of contrast material, and high-quality radiographic imaging.
Factors to be considered when selecting a contrast agent include patient safety, image quality, and cost. Reports of adverse side effects to intravenous contrast agents are limited to two dogs that developed acute and severe systemic reactions to iothalamate meglumine.[2] The features of safety and efficacy are somewhat related to the ionic composition of these materials. High-osmolar ionic compounds include the diatrizoate and iothalamate salts (Conray, Renografin). Low-osmolar nonionic compounds include iohexol (Omnipaque), iopamidol (IsoVue), ioversol (Optiray), iopromide (Ultravist), iobitridol (Xenetix), and iomeprol (Iomeron). Low-osmolar ionic compounds include ioxaglate (Hexabrix). Lower-osmolar agents, both ionic and nonionic, are generally tolerated best by patients, particularly those sensitive to an increase in intravascular volume or having advanced cardiac disease (high-osmolar compounds can generate a greater osmotic load).[3] Nonionic agents also have reduced risk of contrast-related anaphylactoid reactions such as urticaria, flushing, coughing, dyspnea, peripheral edema, and a sudden drop in blood pressure.[4],[5] Contrast-related nephrotoxicity is independent of the contrast agent used but can be reduced by maintaining appropriate patient hydration and minimizing the dose of contrast agent used during the imaging study.[6] Low-osmolar agents are generally considerably more expensive than high-osmolar agents.
Venous angiography is generally less challenging than arterial angiography owing to easier access and lower pressures of the venous system. A small intravenous line is placed in a superficial vein distal to the site of the vascular lesion and contrast material is injected. Images are acquired using mechanical rapid film changers or digitally. The advantages of digital angiography include rapid rate of acquisition, postprocessing capabilities, and reduced exposure to radiation.[1] Digital subtraction angiography may be employed to cancel out portions of an image and thereby improve visualization of structures of interest. Computed tomography (CT) angiography is a fast and invasive procedure that fills simultaneous venous structures with a single peripheral venous injection and has replaced conventional venous angiography in people in most applications. Helical CT and three-dimensional CT angiography have been used in dogs to identify portosystemic vasculature and the identification of vascular shunts.

Answer 3

TECHNIQUES USED TO EVALUATE VENOUS AND LYMPHATIC DISEASE

Angiography

Angiography is the gold standard for evaluating peripheral vascular diseases due to its ability to characterize and visualize normal and abnormal vascular anatomy.[1] Diagnostic outcome requires careful attention to three important elements: selection of radiopaque contrast agent, technique for vascular delivery of contrast material, and high-quality radiographic imaging.
Factors to be considered when selecting a contrast agent include patient safety, image quality, and cost. Reports of adverse side effects to intravenous contrast agents are limited to two dogs that developed acute and severe systemic reactions to iothalamate meglumine.[2] The features of safety and efficacy are somewhat related to the ionic composition of these materials. High-osmolar ionic compounds include the diatrizoate and iothalamate salts (Conray, Renografin). Low-osmolar nonionic compounds include iohexol (Omnipaque), iopamidol (IsoVue), ioversol (Optiray), iopromide (Ultravist), iobitridol (Xenetix), and iomeprol (Iomeron). Low-osmolar ionic compounds include ioxaglate (Hexabrix). Lower-osmolar agents, both ionic and nonionic, are generally tolerated best by patients, particularly those sensitive to an increase in intravascular volume or having advanced cardiac disease (high-osmolar compounds can generate a greater osmotic load).[3] Nonionic agents also have reduced risk of contrast-related anaphylactoid reactions such as urticaria, flushing, coughing, dyspnea, peripheral edema, and a sudden drop in blood pressure.[4],[5] Contrast-related nephrotoxicity is independent of the contrast agent used but can be reduced by maintaining appropriate patient hydration and minimizing the dose of contrast agent used during the imaging study.[6] Low-osmolar agents are generally considerably more expensive than high-osmolar agents.
Venous angiography is generally less challenging than arterial angiography owing to easier access and lower pressures of the venous system. A small intravenous line is placed in a superficial vein distal to the site of the vascular lesion and contrast material is injected. Images are acquired using mechanical rapid film changers or digitally. The advantages of digital angiography include rapid rate of acquisition, postprocessing capabilities, and reduced exposure to radiation.[1] Digital subtraction angiography may be employed to cancel out portions of an image and thereby improve visualization of structures of interest. Computed tomography (CT) angiography is a fast and invasive procedure that fills simultaneous venous structures with a single peripheral venous injection and has replaced conventional venous angiography in people in most applications. Helical CT and three-dimensional CT angiography have been used in dogs to identify portosystemic vasculature and the identification of vascular shunts.

Question 4

These techniques are often selected to detect venous clots (appearing as vascular filling defects) or stenosis. The presence of prolific collateral vasculature can indicate chronic obstruction. Contrast venography of the cranial and caudal vena cava can be performed to assess caval patency, which may be affected by a variety of neoplastic, compressive, or thrombotic disorders.
Lymphangiography helps to permit local assessment of the lymphatic system. The technique of indirect lymphangiography relies on a contrast agent infused into tissue, to be selectively absorbed and transported through lymphatic channels.[9] Direct lymphography is more challenging (unless lymphangiectases have formed) but provides superior results when successfully performed. Selective lymphatic cannulation requires aseptic cutdown over the lymphatic region of interest (note—the identification of lymphangiectases may be facilitated by subcutaneous injection of vital dyes [e.g., 3% Evans blue dye or 11% patent blue violet] into the toe web. By selective resorption of these dyes, the main lymphatic channels proximal to the metacarpus or metatarsus become grossly outlined). The lymphatic vessel is then cannulated with a 27- or 30-gauge needle or a special lymphatic cannula.[9] An iodine-containing soluble contrast medium such as sodium and meglumine diatrizoate (Renografin, Hypaque) is injected slowly into the vessel. Because water-soluble contrast media rapidly diffuse through lymphatic walls into surrounding tissues, the radiographic detail is blurred unless radiographs are taken shortly after dye injection. Alternatively, oily iodine-containing contrast agents (Lipiodol) are used, reducing leakage of contrast from the lymphatic vessels. The oily contrast agents are sequestered within the lymphatics and lymph nodes along the draining pathways.[1] Patency of the lymphatic channels can be appreciated in addition to the size of regional lymph nodes. Metastatic disease to the lymph nodes or granulomas appears as filling defects within the contrast-filled node. Lymphangiography can also be used to identify the location of lymphatic leakage and thoracic duct location in small animals with chylous effusion.[10]

Answer 4

These techniques are often selected to detect venous clots (appearing as vascular filling defects) or stenosis. The presence of prolific collateral vasculature can indicate chronic obstruction. Contrast venography of the cranial and caudal vena cava can be performed to assess caval patency, which may be affected by a variety of neoplastic, compressive, or thrombotic disorders.
Lymphangiography helps to permit local assessment of the lymphatic system. The technique of indirect lymphangiography relies on a contrast agent infused into tissue, to be selectively absorbed and transported through lymphatic channels.[9] Direct lymphography is more challenging (unless lymphangiectases have formed) but provides superior results when successfully performed. Selective lymphatic cannulation requires aseptic cutdown over the lymphatic region of interest (note—the identification of lymphangiectases may be facilitated by subcutaneous injection of vital dyes [e.g., 3% Evans blue dye or 11% patent blue violet] into the toe web. By selective resorption of these dyes, the main lymphatic channels proximal to the metacarpus or metatarsus become grossly outlined). The lymphatic vessel is then cannulated with a 27- or 30-gauge needle or a special lymphatic cannula.[9] An iodine-containing soluble contrast medium such as sodium and meglumine diatrizoate (Renografin, Hypaque) is injected slowly into the vessel. Because water-soluble contrast media rapidly diffuse through lymphatic walls into surrounding tissues, the radiographic detail is blurred unless radiographs are taken shortly after dye injection. Alternatively, oily iodine-containing contrast agents (Lipiodol) are used, reducing leakage of contrast from the lymphatic vessels. The oily contrast agents are sequestered within the lymphatics and lymph nodes along the draining pathways.[1] Patency of the lymphatic channels can be appreciated in addition to the size of regional lymph nodes. Metastatic disease to the lymph nodes or granulomas appears as filling defects within the contrast-filled node. Lymphangiography can also be used to identify the location of lymphatic leakage and thoracic duct location in small animals with chylous effusion.[10]

Question 5

CT lymphangiography has been used in people to evaluate the lymphatic structures and has been also used in dogs to evaluate the thoracic duct anatomy prior to surgery. Improved identification of lymphatic branches and digital subtraction of superimposing anatomic structures are two benefits seen with CT lymphangiography over radiographic lymphangiography.[10]

Answer 5

CT lymphangiography has been used in people to evaluate the lymphatic structures and has been also used in dogs to evaluate the thoracic duct anatomy prior to surgery. Improved identification of lymphatic branches and digital subtraction of superimposing anatomic structures are two benefits seen with CT lymphangiography over radiographic lymphangiography.[10]

Question 6

Diagnostic Ultrasound

Ultrasound imaging provides a direct, noninvasive technique for assessing anatomic abnormalities, vascular patency, and function.[11],[12] Ultrasound can aid in the diagnosis of venous thrombosis, aneurysms, traumatic vascular disease, and compression of vascular structures from local disease processes.
Duplex ultrasonography incorporates gray-scale two-dimensional imaging, with pulsed and color flow Doppler techniques. Thrombi, foreign bodies, compression, and abnormal vascular anatomy can be identified with two-dimensional imaging. Color Doppler superimposed on the two-dimensional image can further help define anatomy and identify turbulence associated with vascular malformation and stenotic lesions.[13]

Answer 6

Diagnostic Ultrasound

Ultrasound imaging provides a direct, noninvasive technique for assessing anatomic abnormalities, vascular patency, and function.[11],[12] Ultrasound can aid in the diagnosis of venous thrombosis, aneurysms, traumatic vascular disease, and compression of vascular structures from local disease processes.
Duplex ultrasonography incorporates gray-scale two-dimensional imaging, with pulsed and color flow Doppler techniques. Thrombi, foreign bodies, compression, and abnormal vascular anatomy can be identified with two-dimensional imaging. Color Doppler superimposed on the two-dimensional image can further help define anatomy and identify turbulence associated with vascular malformation and stenotic lesions.[13]

Question 7

DISEASES OF VEINS

Diseases of the venous system frequently cause …….. clinical problems, despite the fact that veins are commonly affected by or involved in trauma, thromboembolism, edema, local inflammation, and septic processes. Many conditions, however, often go unrecognized. Venous disorders include………..?

Answer 7

DISEASES OF VEINS

Diseases of the venous system frequently cause minor clinical problems, despite the fact that veins are commonly affected by or involved in trauma, thromboembolism, edema, local inflammation, and septic processes. Many conditions, however, often go unrecognized.

Venous disorders include traumatic injuries, superficial and deep phlebitis and thrombosis (thrombophlebitis), catheter embolization, aneurysms, venous compression syndromes, and varicose.

Question 8

Venous thrombi formed in the venous circulation under low blood flow conditions are composed of …….. and ………….. (Figure 256-1) and have been termed “……… thrombi.”

Answer 8

Venous thrombi formed in the venous circulation under low blood flow conditions are composed of fibrin and erythrocytes (Figure 256-1) and have been termed “red thrombi.”

Question 9

Venous thrombosis frequently causes fewer clinical abnormalities than arterial thrombosis and, consequently, is often undetected.

Deep venous thrombosis, a major risk factor for …………………. thromboembolism in over 90% of cases in humans, is ………… to be a risk factor for pulmonary thromboembolism in animals.

Answer 9

Venous thrombosis frequently causes fewer clinical abnormalities than arterial thrombosis and, consequently, is often undetected.

Deep venous thrombosis, a major risk factor for pulmonary thromboembolism in over 90% of cases in humans, is not known to be a risk factor for pulmonary thromboembolism in animals.

Question 10

Pulmonary thromboembolism (PTE) is a common and often life-threatening complication associated with a variety of ……………….and ……………. diseases. A thrombus formed in the ………… heart or the …………….. or ………… venous system can embolize to the pulmonary arterial vasculature.

Answer 10

Pulmonary thromboembolism (PTE) is a common and often life-threatening complication associated with a variety of systemic and metabolic diseases. A thrombus formed in the right heart or the peripheral or central venous system can embolize to the pulmonary arterial vasculature.

Question 11

PTE occurs in several disease states associated with hypercoagulability including ………..syndrome, …………., immune-mediated ………….. ……………., ………………….., ……………… disease, sepsis, ……………………………., ………….. disease, and ………………..

Answer 11

nephrotic syndrome,
hyperadrenocorticism,
immune-mediated hemolytic anemia,
thrombocytosis,
cardiac disease,
sepsis,
disseminated intravascular coagulation,
heartworm disease,
neoplasia.

Question 12

………………… III deficiency may be involved in thrombogenesis as part of a number of these diseases.

For example, destruction of red blood cells in immune-mediated hemolytic anemia releases ………………. substances.

Answer 12

Antithrombin III deficiency may be involved in thrombogenesis as part of a number of these diseases.

For example, destruction of red blood cells in immune-mediated hemolytic anemia releases thrombogenic substances.

Question 13

Antithrombin III inactivates ………….. and other ………………, and only mild reduction in ………… can result in thrombosis or thromboembolism.

Answer 13

Antithrombin III inactivates thrombin and other clotting factors, and only mild reduction in AT-III can result in thrombosis or thromboembolism.

Question 14

A deficiency of AT-III can be secondary to decreased ………… (e.g., congenital), increased …………. (e.g., DIC), loss of …………………………. from the intravascular compartment (e.g., nephrotic syndrome), and increased …………… catabolism (e.g., Cushing’s disease).

Answer 14

A deficiency of AT-III can be secondary to decreased synthesis (e.g., congenital), increased consumption (e.g., DIC), loss of antithrombin from the intravascular compartment (e.g., nephrotic syndrome), and increased protein catabolism (e.g., Cushing’s disease).

Question 15

Protein … and protein …. are vitamin K–dependent protein factors and major inhibitors of the ……………………

……………… of both of these proteins have been associated with clinical thrombotic disorders in humans.

Answer 15

Protein C and protein S are vitamin K–dependent protein factors and major inhibitors of the procoagulant system.

Deficiencies of both of these proteins have been associated with clinical thrombotic disorders in humans.

Question 16

The presence of multiple concurrent disorders in patients with thromboembolism is common. For example, 47% of cats with necropsy confirmed PTE had multiple concurrent predisposing disorders.[24] PTE is covered in detail in Chapter 233.

Answer 16

The presence of multiple concurrent disorders in patients with thromboembolism is common. For example, 47% of cats with necropsy confirmed PTE had multiple concurrent predisposing disorders.[24] PTE is covered in detail in Chapter 233.

Question 17

Varicosis and ulceration are rare in dogs and cats. When detected, they often accompany arteriovenous fistulas. Cutaneous phlebectasia is a benign lesion sometimes erroneously called telangiectasis. It is reported almost exclusively in dogs with spontaneous or iatrogenic Cushing’s syndrome. Phlebectasia is an abnormal dilatation, extension, or reduplication of veins or capillaries or a combination of these changes.

Answer 17

Varicosis and ulceration are rare in dogs and cats. When detected, they often accompany arteriovenous fistulas. Cutaneous phlebectasia is a benign lesion sometimes erroneously called telangiectasis. It is reported almost exclusively in dogs with spontaneous or iatrogenic Cushing’s syndrome. Phlebectasia is an abnormal dilatation, extension, or reduplication of veins or capillaries or a combination of these changes.

Question 18

Venous perforation or blunt trauma to veins is usually well tolerated because rapid clotting results in venous occlusion. If when venous occlusion or venous severance is severe, however, resultant edema and cyanosis are usually temporary because of collateral circulation. If all veins draining an area are compromised, marked edema and necrosis can ensue. Blunt trauma has been associated with caudal vena caval obstruction or kinking of the intrathoracic caudal vena cava and ascites.

Answer 18

Venous perforation or blunt trauma to veins is usually well tolerated because rapid clotting results in venous occlusion. If when venous occlusion or venous severance is severe, however, resultant edema and cyanosis are usually temporary because of collateral circulation. If all veins draining an area are compromised, marked edema and necrosis can ensue. Blunt trauma has been associated with caudal vena caval obstruction or kinking of the intrathoracic caudal vena cava and ascites.

Question 19

Venous malformations have been previously referred to as cavernous hemangiomas. They can be localized or extensive and appear as cystic dilation of blood vessels. They generally permit only low blood flow and small lesions are generally asymptomatic. Expansion of the lesion may occur, however, especially following trauma. Thrombosis may occur due to sluggish blood flow, resulting in local swelling and tenderness. Larger lesions in dependent areas may enlarge, causing significant vascular dilation. This may result in changes in skin color, ulceration, and hemorrhage. Affected area appears as a warm, soft, compressible mass. No thrills or bruits are present due to the low flow. Pain may result from pressure exerted on deep tissues and nerves. Diagnosis is made using history, physical examination, and ultrasound. Venography may be necessary to define the lesion. Symptomatic therapy using light, compressive wraps is sometimes helpful for acute management. Surgical excision of affected vessels is occasionally required, but complete resection is difficult and local recurrence is common.

Answer 19

Venous malformations have been previously referred to as cavernous hemangiomas. They can be localized or extensive and appear as cystic dilation of blood vessels. They generally permit only low blood flow and small lesions are generally asymptomatic. Expansion of the lesion may occur, however, especially following trauma. Thrombosis may occur due to sluggish blood flow, resulting in local swelling and tenderness. Larger lesions in dependent areas may enlarge, causing significant vascular dilation. This may result in changes in skin color, ulceration, and hemorrhage. Affected area appears as a warm, soft, compressible mass. No thrills or bruits are present due to the low flow. Pain may result from pressure exerted on deep tissues and nerves. Diagnosis is made using history, physical examination, and ultrasound. Venography may be necessary to define the lesion. Symptomatic therapy using light, compressive wraps is sometimes helpful for acute management. Surgical excision of affected vessels is occasionally required, but complete resection is difficult and local recurrence is common.

Question 20

Venous aneurysms are rare in veterinary medicine with only a few reported cases. Two cases have been identified in the dog: one case report of a dog with an aneurysm of the jugular, linguofacial, and maxillary veins and a second dog with a cranial vena cava aneurysm.[28],[29] In both cases, these lesions were considered to be secondary to a congenital vascular anomaly and not associated with an obstructive or traumatic process. Thrombosis commonly follows blunt trauma and perforating injuries, particularly with venipuncture or prolonged venous catheterization (Figure 256-2)

Answer 20

Venous aneurysms are rare in veterinary medicine with only a few reported cases. Two cases have been identified in the dog: one case report of a dog with an aneurysm of the jugular, linguofacial, and maxillary veins and a second dog with a cranial vena cava aneurysm.[28],[29] In both cases, these lesions were considered to be secondary to a congenital vascular anomaly and not associated with an obstructive or traumatic process. Thrombosis commonly follows blunt trauma and perforating injuries, particularly with venipuncture or prolonged venous catheterization (Figure 256-2)

Question 21

…………………. is a major cause of intimal damage leading to thrombosis. The thrombosis is usually of little local consequence. However, emboli may be carried to the lung and cause PTE. In most animals, blood clots carried to the lung are rapidly lysed and cause no problems. However, when inflammatory diseases, dehydration, or circulatory failure occurs, clot formation may continue in the pulmonary vessels and lead to vascular occlusion, severe dyspnea, pain, and death.

Answer 21

Phlebitis is a major cause of intimal damage leading to thrombosis. The thrombosis is usually of little local consequence. However, emboli may be carried to the lung and cause PTE. In most animals, blood clots carried to the lung are rapidly lysed and cause no problems. However, when inflammatory diseases, dehydration, or circulatory failure occurs, clot formation may continue in the pulmonary vessels and lead to vascular occlusion, severe dyspnea, pain, and death.

Question 22

In ……………………… thrombophlebitis, bacterial emboli may be carried to the lungs and cause thromboembolic pneumonia. Spontaneous venous thrombosis is rare, although portal vein thrombosis has been reported. Clinical signs include ascites, peripheral pitting edema, and portosystemic shunting.

Answer 22

In infectious thrombophlebitis, bacterial emboli may be carried to the lungs and cause thromboembolic pneumonia. Spontaneous venous thrombosis is rare, although portal vein thrombosis has been reported. Clinical signs include ascites, peripheral pitting edema, and portosystemic shunting.

Question 23

Embolization of severed intravascular catheter……………. is an occasional complication of intravenous catheter placement. In humans, reported complications of catheter embolization include perforation of cardiac walls, endocarditis, pulmonary embolism, and severe arrhythmias.

Therefore, it is generally considered prudent to removal catheter fragments. Nonsurgical, transvenous removal of catheter fragments using loop-snare catheters, forceps, and basket catheters have been described. Whenever possible, however, steps should be taken to avoid situations predisposing to catheter fragmentation including inadequate restraint during catheter placement, withdrawal of catheters through their placement needles during repositioning, failure to properly secure catheter to the patient, and inadvertent severing of catheters during bandage changes.

Answer 23

Embolization of severed intravascular catheter fragments is an occasional complication of intravenous catheter placement. In humans, reported complications of catheter embolization include perforation of cardiac walls, endocarditis, pulmonary embolism, and severe arrhythmias.

Therefore, it is generally considered prudent to removal catheter fragments. Nonsurgical, transvenous removal of catheter fragments using loop-snare catheters, forceps, and basket catheters have been described. Whenever possible, however, steps should be taken to avoid situations predisposing to catheter fragmentation including inadequate restraint during catheter placement, withdrawal of catheters through their placement needles during repositioning, failure to properly secure catheter to the patient, and inadvertent severing of catheters during bandage changes.

Question 24

Phlebitis can occur from a local inflammatory process extending to the veins or can originate from a venous intimal lesion. Common causes of venous intimal lesions are perivenous injection of irritating drugs, infusion of large amounts of fluid, and long-term placement of intravenous catheters. Infusion-related phlebitis occurs in three forms: (1) chemical (injury to vein by irritating drugs), (2) physical (trauma to the intima by catheters, needles, hypertonicity or particulate matter in infused fluids), and (3) microbial (infected fluids, skin, or catheter tip). Sterile or septic thrombophlebitis may result. It usually remains localized and is characterized by pain, swelling, and exudation (Figure 256-3). Patients with serious illnesses or compromised immune systems, however, may develop sepsis, thromboembolic pneumonia, or endocarditis.

Answer 24

Phlebitis can occur from a local inflammatory process extending to the veins or can originate from a venous intimal lesion. Common causes of venous intimal lesions are perivenous injection of irritating drugs, infusion of large amounts of fluid, and long-term placement of intravenous catheters. Infusion-related phlebitis occurs in three forms: (1) chemical (injury to vein by irritating drugs), (2) physical (trauma to the intima by catheters, needles, hypertonicity or particulate matter in infused fluids), and (3) microbial (infected fluids, skin, or catheter tip). Sterile or septic thrombophlebitis may result. It usually remains localized and is characterized by pain, swelling, and exudation (Figure 256-3). Patients with serious illnesses or compromised immune systems, however, may develop sepsis, thromboembolic pneumonia, or endocarditis.

Question 25

In cases of venous occlusion, clinical signs depend on?

Answer 25

In cases of venous occlusion, clinical signs depend on the anatomic location, extent, and duration of the obstruction.

Question 26

Acute obstruction of centrally located and deep veins causes edema, cyanosis, discomfort, and venous dilatation distal to the obstruction site. Acute obstruction of centrally located and deep veins causes

Answer 26

Edema, cyanosis, discomfort, and venous dilatation distal to the obstruction site.

Question 27

Obstruction of the cranial vena cava causes?

Answer 27

Edema in the neck, head, front limbs, and dependent portions of the chest wall (Figure 256-4).

Question 28

Pleural effusion commonly results from ...................obstruction. Clinical disorders of the intrathoracic caudal vena cava have been reported (Figure 256-5).[26]

Answer 28

Pleural effusion commonly results from central venous obstruction. Clinical disorders of the intrathoracic caudal vena cava have been reported (Figure 256-5).[26]

Question 29

Obstructions of the ........... or ............ cause edema of the hindlimbs and the scrotum. Clinical signs depend upon ............... vessel reserve and capacity of regional ................

Answer 29

Obstructions of the renal or pelvic area cause edema of the hindlimbs and the scrotum. Clinical signs depend upon collateral vessel reserve and capacity of regional lymphatics.

Question 30

In addition to thrombosis, common causes of venous obstruction include.....?

Answer 30

Invasive malignant processes and venous compression by abscesses, hematomas, tumors, and lymphadenopathy.

Question 31

A number of tumors have a tendency for venous invasion, including chemodectomas, adrenal tumors, and hemangiosarcomas. Angiography may indicate the occlusive or compressive lesion and/or highlight increased collateral circulation (Figure 256-6). Diagnostic ultrasonography can often detect masses or flow disturbances. The prognosis and therapy of venous obstruction depend on the primary disease.

Answer 31

A number of tumors have a tendency for venous invasion, including chemodectomas, adrenal tumors, and hemangiosarcomas. Angiography may indicate the occlusive or compressive lesion and/or highlight increased collateral circulation (Figure 256-6). Diagnostic ultrasonography can often detect masses or flow disturbances. The prognosis and therapy of venous obstruction depend on the primary disease.

Question 32

DISEASES OF THE PERIPHERAL LYMPHATICS The lymphatic system plays a critical role in regulating body fluid volume and immune function. Lymphatics originate within the interstitium as specialized endothelial-lined capillaries transporting ..........., ............., and ............... particles back into the venous system.

Answer 32

DISEASES OF THE PERIPHERAL LYMPHATICS The lymphatic system plays a critical role in regulating body fluid volume and immune function. Lymphatics originate within the interstitium as specialized endothelial-lined capillaries transporting fluid, solutes, and macromolecular particles back into the venous system.

Question 33

Fluid, protein, cells, and macromolecular particles from the interstitial space empty into the initial lymphatics composed of a series of small lymphatic capillaries that begin .............. in the tissues. The lymph then flows through a system of lymphatic vessels, which progressively increase in diameter. As lymph flows centrally it passes through at least one lymph node before emptying into larger lymphatic............

Answer 33

Fluid, protein, cells, and macromolecular particles from the interstitial space empty into the initial lymphatics composed of a series of small lymphatic capillaries that begin blindly in the tissues. The lymph then flows through a system of lymphatic vessels, which progressively increase in diameter. As lymph flows centrally it passes through at least one lymph node before emptying into larger lymphatic trunks.

Question 34

The deep trunks unite to form two major lymphatic vessels: the ................ and ................ducts. The ...............drains most of the body and returns fluid into the venous system at the ................. vein or the ....................... vein. The right lymphatic duct drains the ..................................................

Answer 34

The deep trunks unite to form two major lymphatic vessels: the thoracic and right lymphatic ducts. The thoracic duct drains most of the body and returns fluid into the venous system at the brachycephalic vein or the left subclavian vein. The right lymphatic duct drains the right side of the head and neck and right forelimb.

Question 35

Lymphatic vessels contain many .............. between individual ................ cells, which are connected to the surrounding extracellular matrix by reticular fibers and collagen. These junctions open when tissue .................. pressure becomes elevated and the anchoring filaments stretch, allowing fluid to move into the vessel. As the fluid is cleared from the interstitium, the connecting ...........contract and the junctions between the endothelial cells close. The opening and closing of these junctions allow them to act as ...................... preventing the backflow of lymph into the interstitium. The larger vessels of the lymphatic system have progressively ............ open junctions, increasingly ................. walls, and frequent intralymphatic ............... that also prevent backflow of lymph. The action of .................. contraction along with intrinsic contractility of the lymphatic vessels aids in the movement of lymph through the lymphatic system.

Answer 35

Lymphatic vessels contain many junctions between individual endothelial cells, which are connected to the surrounding extracellular matrix by reticular fibers and collagen. These junctions open when tissue hydrostatic pressure becomes elevated and the anchoring filaments stretch, allowing fluid to move into the vessel. As the fluid is cleared from the interstitium, the connecting fibers contract and the junctions between the endothelial cells close. The opening and closing of these junctions allow them to act as inlet valves preventing the backflow of lymph into the interstitium. The larger vessels of the lymphatic system have progressively fewer open junctions, increasingly muscular walls, and frequent intralymphatic valves that also prevent backflow of lymph. The action of external muscular contraction along with intrinsic contractility of the lymphatic vessels aids in the movement of lymph through the lymphatic system.

Question 36

Lymph is filtered by at least one lymph node before entering the venous circulation. While in the lymph node, the lymph is in contact with the blood circulation and approximately ................... fluid is drained before leaving into the larger lymphatic ducts. In addition to its transport function, the lymph system plays a major role in the ................... responses to infectious agents. It serves as a filtering system to impede the spread of microorganisms and neoplastic cells. The cellular components, in particular the lymphocytes, are indispensable for immunologic reactions and antibody formation.

Answer 36

Lymph is filtered by at least one lymph node before entering the venous circulation. While in the lymph node, the lymph is in contact with the blood circulation and approximately half of the fluid is drained before leaving into the larger lymphatic ducts. In addition to its transport function, the lymph system plays a major role in the immunologic responses to infectious agents. It serves as a filtering system to impede the spread of microorganisms and neoplastic cells. The cellular components, in particular the lymphocytes, are indispensable for immunologic reactions and antibody formation.

Question 37

Lymphatic disorders can be subdivided into....?

Answer 37

Those of internal organs, such as intestinal lymphangiectasis, and peripheral lymphatic disorders. Several lymphatic diseases including lymphedema, intestinal lymphangiectasia, chylothorax, lymphadenitis, lymphocysts, lymphoma, lymphangioma, and lymphangiosarcoma have been recognized in animals. Types and causes of peripheral lymphatic disorders are summarized in Box 256-2.

Question 38

INFLAMMATORY LYMPHATIC DISORDERS (LYMPHANGITIS AND LYMPHADENITIS) Lymphangitis and lymphadenitis often occur secondary to local inflammation, particularly involving the skin, mucous membranes, and subcutaneous tissues. Lymphangitis can also result from bacterial or fungal infection or adjacent neoplastic and inflammatory disease. Lymphatics may be affected and occluded as they drain inflammatory agents and their by-products from tissue spaces. In lymph nodes, microorganisms are .................. and inactivated or killed by .............. and .............mechanisms.

Answer 38

INFLAMMATORY LYMPHATIC DISORDERS (LYMPHANGITIS AND LYMPHADENITIS) Lymphangitis and lymphadenitis often occur secondary to local inflammation, particularly involving the skin, mucous membranes, and subcutaneous tissues. Lymphangitis can also result from bacterial or fungal infection or adjacent neoplastic and inflammatory disease. Lymphatics may be affected and occluded as they drain inflammatory agents and their by-products from tissue spaces. In lymph nodes, microorganisms are phagocytized and inactivated or killed by humoral and cellular mechanisms.

Question 39

During this process, lymph nodes may become ................., enlarged, warm, and painful. Affected limbs may be locally swollen and lameness can result. Pyrexia, anorexia, and depression are common and leukocytosis may be present with acute, severe lymphangitis. Lymphangitis may become .............. when associated with a granulomatous or static lesion such as a foreign body or with unsuccessfully treated acute inflammation. Persistence of inflammatory edema results in ........................cell proliferation, which in turn can cause irreversible thickening of skin and subcutis.

Answer 39

During this process, lymph nodes may become obstructed, enlarged, warm, and painful. Affected limbs may be locally swollen and lameness can result. Pyrexia, anorexia, and depression are common and leukocytosis may be present with acute, severe lymphangitis. Lymphangitis may become chronic when associated with a granulomatous or static lesion such as a foreign body or with unsuccessfully treated acute inflammation. Persistence of inflammatory edema results in mesenchymal cell proliferation, which in turn can cause irreversible thickening of skin and subcutis.

Question 40

LYMPHEDEMA Lymphedema refers to an ................................. This term should not be used for other forms of edema, such as edema related to venous obstruction or generalized edema related to hypoproteinemia.

Answer 40

LYMPHEDEMA Lymphedema refers to an accumulation of fluid in the interstitial space resulting from abnormal lymphatic drainage.[37] This term should not be used for other forms of edema, such as edema related to venous obstruction or generalized edema related to hypoproteinemia.

Question 41

Lymphedema may result when capillary filtration exceeds the resorptive capacity of the veins and lymphatics. The .................- rich fluid (2 to 5 g/dL) causes a high ..........gradient and exacerbates fluid accumulation.

Answer 41

Lymphedema may result when capillary filtration exceeds the resorptive capacity of the veins and lymphatics. The protein-rich fluid (2 to 5 g/dL) causes a high osmotic gradient and exacerbates fluid accumulation.[38]

Question 42

Numerous classification schemes have been used to categorize lymphedema. Commonly used etiologic categories of lymphedema include....?

Answer 42

Overload, inadequate collection into lymphatic capillaries, abnormal lymphatic contractility, insufficient lymphatics, lymph node obstruction, and main lymphatic ductal defects.

Question 43

Traditionally, clinical effort is undertaken to differentiate primary versus secondary lymphedema. Primary lymphedema refers ........................... Secondary lymphedema refers to disease in the lymphatic vessels or lymph nodes due to ........................

Answer 43

Traditionally, clinical effort is undertaken to differentiate primary versus secondary lymphedema. Primary lymphedema refers to an abnormality of the lymphatic vessels or lymph nodes. Secondary lymphedema refers to disease in the lymphatic vessels or lymph nodes due to a different disease process. Secondary lymphedema can occur as a result of neoplasia, surgery, trauma, parasites, radiation therapy, or infection and is more common than primary lymphedema. Distinguishing between primary and secondary lymphedema is often difficult. A disease process involving a lymph node can result in fibrosis and obstruction with secondary lymphedema developing.

Question 44

Primary Lymphedema Primary lymphedema can result from three principle morphologic and functional abnormalities including...?

Answer 44

(1) abnormalities of large vessels including aplasia or hypoplasia of the thoracic duct and cisterna chyli, (2) aplasia of the peripheral lymphatics or congenital valvular incompetence, and (3) lymph node fibrosis or a deficient lymph node size and number.

Question 45

Primary Lymphedema: Lymphedema caused by aplasia, hypoplasia, or dysplasia of proximal lymph channels and/or popliteal lymph nodes occurs most often in the hindlimbs of young dogs (Figure 256-7). The edema can be transient, observed only during the juvenile period, or permanent. Mild cases are restricted to the hindlimbs, whereas severe cases may progress to whole body edema.[43-46] Although the condition is frequently bilateral, one limb is often more swollen than the other. A number of cases of suspected congenital lymphedema have been reported.[45-48] Reported breeds include Bulldogs, Poodles, Old English Sheepdogs, and Labrador Retrievers, although it is not clear whether these breeds are at increased risk.

Answer 45

Lymphedema caused by aplasia, hypoplasia, or dysplasia of proximal lymph channels and/or popliteal lymph nodes occurs most often in the hindlimbs of young dogs (Figure 256-7). The edema can be transient, observed only during the juvenile period, or permanent. Mild cases are restricted to the hindlimbs, whereas severe cases may progress to whole body edema.[43-46] Although the condition is frequently bilateral, one limb is often more swollen than the other. A number of cases of suspected congenital lymphedema have been reported.[45-48] Reported breeds include Bulldogs, Poodles, Old English Sheepdogs, and Labrador Retrievers, although it is not clear whether these breeds are at increased risk.

Question 46

Primary Lymphedema: The history may identify chronic limb swelling since birth or edema appearing later in life. The swelling represents a pitting edema of varying magnitude that is neither too warm nor cold. The edema is not usually accompanied by lameness or pain unless there is massive enlargement or cellulitis. Growth and activity are usually normal but rest and limb massage do not typically reduce the severity of edema. Total plasma protein, serum protein electrophoresis, hemogram, and blood chemistry are generally ........................... The diagnosis of primary lymphedema is based on history (age of onset, disease progression, affected limbs, and distribution of edema) and clinical signs. Previous surgery, trauma, or infections should also be noted. Radiographic lymphography may be necessary to confirm the diagnosis in subtle cases and is helpful in determining morphology of anomalous lymphatic systems (Figure 256-8).

Answer 46

The history may identify chronic limb swelling since birth or edema appearing later in life. The swelling represents a pitting edema of varying magnitude that is neither too warm nor cold. The edema is not usually accompanied by lameness or pain unless there is massive enlargement or cellulitis. Growth and activity are usually normal but rest and limb massage do not typically reduce the severity of edema. Total plasma protein, serum protein electrophoresis, hemogram, and blood chemistry are generally unremarkable. The diagnosis of primary lymphedema is based on history (age of onset, disease progression, affected limbs, and distribution of edema) and clinical signs. Previous surgery, trauma, or infections should also be noted. Radiographic lymphography may be necessary to confirm the diagnosis in subtle cases and is helpful in determining morphology of anomalous lymphatic systems (Figure 256-8).

Question 47

The prognosis for resolution of congenital lymphedema is guarded and depends on the etiology. Occasionally, dogs who develop hindlimb edema during the neonatal period may improve spontaneously. More frequently, dogs with severe edema of the limbs and trunk succumb during the first few weeks after birth.[43] Chronic lymphatic vessel dilation leads to loss of contractility and permanent lymphatic valvular dysfunction. Metabolic by-products accumulate and lead to collagen deposition and fibrosis. Complications such as abrasions and infection often develop. Dogs with primary lymphedema should not be used for breeding. Test matings of dogs with congenital lymphedema support the hypothesis of autosomal dominant inheritance with variable expression.

Answer 47

The prognosis for resolution of congenital lymphedema is guarded and depends on the etiology. Occasionally, dogs who develop hindlimb edema during the neonatal period may improve spontaneously. More frequently, dogs with severe edema of the limbs and trunk succumb during the first few weeks after birth.[43] Chronic lymphatic vessel dilation leads to loss of contractility and permanent lymphatic valvular dysfunction. Metabolic by-products accumulate and lead to collagen deposition and fibrosis. Complications such as abrasions and infection often develop. Dogs with primary lymphedema should not be used for breeding. Test matings of dogs with congenital lymphedema support the hypothesis of autosomal dominant inheritance with variable expression.

Question 48

Secondary Lymphedema Persistent lymphedema occurs only after .......... or ..................of a considerable number of major lymph channels or several sequential lymph nodes with their afferent or efferent lymphatics. Factors that can delay or prevent edema formation include opening of collateral vessels, rerouting of lymph flow through peripheral lymphaticovenous anastomoses and perilymphatic routes of lymph drainage, and increased venous fluid uptake. Secondary lymphedema is often related to a combination of............ and ................obstruction.

Answer 48

Secondary Lymphedema Persistent lymphedema occurs only after destruction or blockage of a considerable number of major lymph channels or several sequential lymph nodes with their afferent or efferent lymphatics. Factors that can delay or prevent edema formation include opening of collateral vessels, rerouting of lymph flow through peripheral lymphaticovenous anastomoses and perilymphatic routes of lymph drainage, and increased venous fluid uptake. Secondary lymphedema is often related to a combination of lymphatic and venous obstruction.

Question 49

Inhibited venous return increases lymphatic ........... by altering Starling's forces toward increased................ accumulation. This overloads the lymphatic capillaries and results in the accumulation of fluid in the...................space. Distal lymphatics may become more ..............., causing loss of valvular competency, stagnation of lymph flow, mural insufficiency, and further accumulation of proteinaceous fluid in subcutaneous tissues.

Answer 49

Inhibited venous return increases lymphatic flow by altering Starling's forces toward increased tissue fluid accumulation. This overloads the lymphatic capillaries and results in the accumulation of fluid in the interstitial space. Distal lymphatics may become more distended, causing loss of valvular competency, stagnation of lymph flow, mural insufficiency, and further accumulation of proteinaceous fluid in subcutaneous tissues.

Question 50

Other common etiologies include posttraumatic or postsurgical interruption of lymphatics or lymph node excision and blockage of lymph nodes and lymph vessels by compression or invasive neoplasms. Lymphedema resulting from local neoplasia is usually a sign of a widely disseminated and highly invasive malignant process.

Answer 50

Other common etiologies include posttraumatic or postsurgical interruption of lymphatics or lymph node excision and blockage of lymph nodes and lymph vessels by compression or invasive neoplasms. Lymphedema resulting from local neoplasia is usually a sign of a widely disseminated and highly invasive malignant process.

Question 51

Clinical signs associated with secondary lymphedema vary depending on the underlying systemic causes. Lymphedema may be localized to the periphery of an extremity (Figure 256-9) or extend proximally to the subcutaneous tissues.[50] The location and severity of obstruction determine the extent of edema formation. For example, sublumbar or intrapelvic obstruction induces bilateral hindlimb edema and edema of the thighs and external genitalia.

Answer 51

Clinical signs associated with secondary lymphedema vary depending on the underlying systemic causes. Lymphedema may be localized to the periphery of an extremity (Figure 256-9) or extend proximally to the subcutaneous tissues.[50] The location and severity of obstruction determine the extent of edema formation. For example, sublumbar or intrapelvic obstruction induces bilateral hindlimb edema and edema of the thighs and external genitalia.

Question 52

Mediastinal masses and thrombosis of the cranial vena cava induce bilateral edema of the front limbs and tissue of the ventral thorax, neck, and head. The clinician must palpate all lymph nodes carefully for enlargement and pain. With bilateral hindlimb edema, it is important to perform rectal or abdominal palpation to assess sublumbar lymph nodes. The prostate and anal region or mammary glands and vaginal area should be carefully inspected for neoplasms, which can lead to obstructive intrapelvic processes.

Answer 52

Mediastinal masses and thrombosis of the cranial vena cava induce bilateral edema of the front limbs and tissue of the ventral thorax, neck, and head. The clinician must palpate all lymph nodes carefully for enlargement and pain. With bilateral hindlimb edema, it is important to perform rectal or abdominal palpation to assess sublumbar lymph nodes. The prostate and anal region or mammary glands and vaginal area should be carefully inspected for neoplasms, which can lead to obstructive intrapelvic processes.

Question 53

Intrapelvic masses should be suspected in all dogs with hindlimb edema and vague signs of sublumbar pain, discomfort during ambulation, or difficulties with defecation or urination. Depending on the type and extent of underlying systemic illness, limb edema may be the only detectable abnormality or may be accompanied by fever, anorexia, and weight loss. Clinicopathologic findings depend on the underlying primary disorder.

Answer 53

Intrapelvic masses should be suspected in all dogs with hindlimb edema and vague signs of sublumbar pain, discomfort during ambulation, or difficulties with defecation or urination. Depending on the type and extent of underlying systemic illness, limb edema may be the only detectable abnormality or may be accompanied by fever, anorexia, and weight loss. Clinicopathologic findings depend on the underlying primary disorder.

Question 54

Diagnosis is based largely on history and clinical examination and is facilitated by diagnostic imaging. Survey radiographs should be taken of suspicious areas, which often include the pelvis or cranial thorax. In a substantial number of cases, soft tissue masses or destructive bony lesions can be detected. Abdominal ultrasonography can provide information about soft tissue masses and readily identifies enlarged lymph nodes and other structures. Lymphography or other imaging techniques may be indicated if the diagnosis remains unclear. Lymphography is often relied upon for definitive diagnosis of lymphatic disorders. In some cases the lymphatics are hypoplastic throughout their course. When aplastic, lymphatics suitable for cannulation and injection of radiocontrast agent may not be found. Failure to outline a lymph node after lymphography is not absolute proof of its absence.[38] Lymphographic features of primary lymphedema include lymph node aplasia and small lymphatics that end blindly or anastomose into collateral vessels around (instead of into) lymph nodes, where they would be normally found.

Answer 54

Diagnosis is based largely on history and clinical examination and is facilitated by diagnostic imaging. Survey radiographs should be taken of suspicious areas, which often include the pelvis or cranial thorax. In a substantial number of cases, soft tissue masses or destructive bony lesions can be detected. Abdominal ultrasonography can provide information about soft tissue masses and readily identifies enlarged lymph nodes and other structures. Lymphography or other imaging techniques may be indicated if the diagnosis remains unclear. Lymphography is often relied upon for definitive diagnosis of lymphatic disorders. In some cases the lymphatics are hypoplastic throughout their course. When aplastic, lymphatics suitable for cannulation and injection of radiocontrast agent may not be found. Failure to outline a lymph node after lymphography is not absolute proof of its absence.[38] Lymphographic features of primary lymphedema include lymph node aplasia and small lymphatics that end blindly or anastomose into collateral vessels around (instead of into) lymph nodes, where they would be normally found.

Question 55

Lymphoscintigraphy is an alternative approach for imaging peripheral lymphatics. This technique requires a gamma-camera system and intradermal injection of high-molecular-weight radiolabeled colloids.[51,54,55] Such equipment and specialized training are not widely available. When compared with conventional lymphography, lymph nodes only appear as “hot spots” preventing adequate assessment of nodal structure.

Answer 55

Lymphoscintigraphy is an alternative approach for imaging peripheral lymphatics. This technique requires a gamma-camera system and intradermal injection of high-molecular-weight radiolabeled colloids.[51,54,55] Such equipment and specialized training are not widely available. When compared with conventional lymphography, lymph nodes only appear as “hot spots” preventing adequate assessment of nodal structure.

Question 56

Differential diagnoses for dogs with edema confined to one limb include inflammation, trauma, vascular obstruction, hemorrhage, cellulitis, phlebitis, and AV fistula. Diagnostic considerations for dogs with edema involving both forelimbs include thrombosis or compression or invasion of the cranial cava by a mediastinal mass. With the latter, edema usually involves the head and neck regions, as well as the limbs. Causes of only bilateral hindlimb edema include obstruction of sublumbar lymph nodes by neoplastic infiltration. If all four limbs are involved, the differential diagnoses should include hypoproteinemia, congestive heart failure, renal failure, or portal hypertension. The close association of lymphatic and venous structures can make it difficult to distinguish between lymphatic and venous obstruction, and both can occur at the same time. Ulceration, dermatitis, cyanosis, weeping varices, and/or fat necrosis are signs of venous obstruction rather than lymph stasis.

Answer 56

Differential diagnoses for dogs with edema confined to one limb include inflammation, trauma, vascular obstruction, hemorrhage, cellulitis, phlebitis, and AV fistula. Diagnostic considerations for dogs with edema involving both forelimbs include thrombosis or compression or invasion of the cranial cava by a mediastinal mass. With the latter, edema usually involves the head and neck regions, as well as the limbs. Causes of only bilateral hindlimb edema include obstruction of sublumbar lymph nodes by neoplastic infiltration. If all four limbs are involved, the differential diagnoses should include hypoproteinemia, congestive heart failure, renal failure, or portal hypertension. The close association of lymphatic and venous structures can make it difficult to distinguish between lymphatic and venous obstruction, and both can occur at the same time. Ulceration, dermatitis, cyanosis, weeping varices, and/or fat necrosis are signs of venous obstruction rather than lymph stasis.

Question 57

Therapy is usually unrewarding. In the early stages of lymphedema medical management is directed to maintaining the patient's comfort and reducing swelling. Infectious disorders require long-term antimicrobial therapy. Some neoplastic conditions may benefit from chemotherapy or radiation therapy. Long-term heavy bandage application (e.g., Robert Jones splint) may encourage lymphatic flow and reduce subcutaneous lymph accumulation. Local topical skin care and intermittent antibiotic therapy are helpful in reducing cellulitis. With the exception of isolated instances, pharmacologic therapies are generally unrewarding. The benzopyrenes (e.g., rutin) are a group of drugs that have been advocated to reduce high-protein lymphedema by stimulating macrophages, promoting proteolysis, and enhancing absorption of protein fragments.[56] Long-term diuretic administration may be contraindicated because after reduction of interstitial fluid, proteins in the residual interstitial space proteins may promote tissue injury.[53] Surgical options may include (1) procedures to facilitate lymph drainage from affected limbs (lymphangioplasty, bridging procedures, shunts, omental transposition) and (2) procedures to excise abnormal tissue. Surgical excision of the subcutaneous edematous tissue should be staged to decrease devascularization.[53] Short-term administration of antiinflammatory agents or diuretics, bandaging, and physical therapy may be helpful in cases of traumatic and postsurgical induced lymphedemas.

Answer 57

Therapy is usually unrewarding. In the early stages of lymphedema medical management is directed to maintaining the patient's comfort and reducing swelling. Infectious disorders require long-term antimicrobial therapy. Some neoplastic conditions may benefit from chemotherapy or radiation therapy. Long-term heavy bandage application (e.g., Robert Jones splint) may encourage lymphatic flow and reduce subcutaneous lymph accumulation. Local topical skin care and intermittent antibiotic therapy are helpful in reducing cellulitis. With the exception of isolated instances, pharmacologic therapies are generally unrewarding. The benzopyrenes (e.g., rutin) are a group of drugs that have been advocated to reduce high-protein lymphedema by stimulating macrophages, promoting proteolysis, and enhancing absorption of protein fragments.[56] Long-term diuretic administration may be contraindicated because after reduction of interstitial fluid, proteins in the residual interstitial space proteins may promote tissue injury.[53] Surgical options may include (1) procedures to facilitate lymph drainage from affected limbs (lymphangioplasty, bridging procedures, shunts, omental transposition) and (2) procedures to excise abnormal tissue. Surgical excision of the subcutaneous edematous tissue should be staged to decrease devascularization.[53] Short-term administration of antiinflammatory agents or diuretics, bandaging, and physical therapy may be helpful in cases of traumatic and postsurgical induced lymphedemas.

Question 58

LYMPHANGIOMA, LYMPHANGIOSARCOMA Lymphangiomas are benign tumors of lymphatic capillaries and are thought to develop when primitive lymphatic sacs fail to establish venous communication.[57] Lymphangiomas can be classified into three categories based on their histologic appearance: (1) capillary lymphangiomas composed of a network of capillary-sized lymphatic channels, (2) cavernous lymphangiomas composed of dilated lymphatics that infiltrate the surrounding tissue, and (3) cystic hygromas (unilocular or multilocular, cystic masses lined by a single layer of endothelium supported by a connective tissue stroma and containing a straw-colored, proteinaceous [1.3 to 4.5 g/dL] fluid).[58] The lesions present as large, fluctuant masses in the subcutaneous, fascial, mediastinal, hepatic, lymph nodes, and retroperitoneal spaces.[59-62] Lymphangiomas have also been diagnosed on the extremities, metacarpal pads, nasopharynx, axilla, inguinal and mammary region, retroperitoneal space, and skin of dogs.[57,63-65] Clinical signs are related to the size, location, and extent of the lymphangioma. They can exert pressure on surrounding structures and may interfere with muscle function, breathing (compression of the trachea), urination, or intestinal function. Lymph may ooze to the skin surface through single or multiple fistulous tracts. Differential diagnoses include other space-occupying masses such as abscesses, enlarged lymph nodes, neoplasms, and congenital cysts of nonlymphogenic origin. The prognosis can be good after appropriate surgical excision, marsupialization, or radiation therapy.[66] Risk of recurrence is high due to inherent inability to identify distinct boundaries.

Answer 58

LYMPHANGIOMA, LYMPHANGIOSARCOMA Lymphangiomas are benign tumors of lymphatic capillaries and are thought to develop when primitive lymphatic sacs fail to establish venous communication.[57] Lymphangiomas can be classified into three categories based on their histologic appearance: (1) capillary lymphangiomas composed of a network of capillary-sized lymphatic channels, (2) cavernous lymphangiomas composed of dilated lymphatics that infiltrate the surrounding tissue, and (3) cystic hygromas (unilocular or multilocular, cystic masses lined by a single layer of endothelium supported by a connective tissue stroma and containing a straw-colored, proteinaceous [1.3 to 4.5 g/dL] fluid).[58] The lesions present as large, fluctuant masses in the subcutaneous, fascial, mediastinal, hepatic, lymph nodes, and retroperitoneal spaces.[59-62] Lymphangiomas have also been diagnosed on the extremities, metacarpal pads, nasopharynx, axilla, inguinal and mammary region, retroperitoneal space, and skin of dogs.[57,63-65] Clinical signs are related to the size, location, and extent of the lymphangioma. They can exert pressure on surrounding structures and may interfere with muscle function, breathing (compression of the trachea), urination, or intestinal function. Lymph may ooze to the skin surface through single or multiple fistulous tracts. Differential diagnoses include other space-occupying masses such as abscesses, enlarged lymph nodes, neoplasms, and congenital cysts of nonlymphogenic origin. The prognosis can be good after appropriate surgical excision, marsupialization, or radiation therapy.[66] Risk of recurrence is high due to inherent inability to identify distinct boundaries.

Question 59

Lymphangiosarcoma originates from lymphatic endothelial cells.[67] It is a rare malignant tumor in dogs and cats, although it is frequently reported secondary to chronic lymphedema in humans.[68-70] A breed or sex predisposition has not been detected, but medium to large breeds may be at highest risk, and both young and older animals are affected.[67-68,71] Metastasis occurs commonly in dogs and cats, although an isolated case without metastasis has been reported.[67],[72] Clinical signs include pitting edema of the extremities, inguinal region, axilla, and head and neck (Figure 256-10).

Answer 59

Lymphangiosarcoma originates from lymphatic endothelial cells.[67] It is a rare malignant tumor in dogs and cats, although it is frequently reported secondary to chronic lymphedema in humans.[68-70] A breed or sex predisposition has not been detected, but medium to large breeds may be at highest risk, and both young and older animals are affected.[67-68,71] Metastasis occurs commonly in dogs and cats, although an isolated case without metastasis has been reported.[67],[72] Clinical signs include pitting edema of the extremities, inguinal region, axilla, and head and neck (Figure 256-10).

Question 60

In a report of 12 cats with lymphangiosarcoma, 9 presented with fast-growing, noncircumscribed subcutaneous masses and the others presented with a thoracic or abdominal mass. In all cats affected, the tumor was invasive and complete surgical resection was not possible.[72] In two additional cats with lymphangiosarcoma, one cat developed regional bony lysis in the affected limb and one cat developed immune-mediated hemolytic anemia.[73] Associated chylous effusions (pleural, abdominal, subcutaneous) have been reported.[74-76] Pulmonary lymphangiosarcoma was diagnosed in one dog presenting with a chylous effusion.[77] Diagnosis is confirmed by obtaining a biopsy specimen. Histologically, tumors of lymphatic endothelial origin are characterized by a neoplastic proliferation of endothelial cells. Immunocytochemical stains have been used to confirm the diagnosis in dogs and cats.[78-80] The identification of the factor VIII-related antigen and vimentin indicates the cells are of endothelial origin. The intensity and distribution of the stain has been used to attempt to differentiate lymphangiosarcomas from hemangiosarcomas but is often inaccurate. Newer specific markers to identify lymphatic endothelial cells have been identified in cats with lymphangiosarcoma.[79],[80] The prognosis with lymphangiosarcoma is poor with a high rate of local recurrence and metastasis. Most animals are euthanized or died due to severe lymphedema, pleural effusion, and/or distant metastases. There is one report with a positive response to mass resection and doxorubicin treatment. Recurrence of the mass or evidence of metastasis was not evident in a 9-month follow-up period.[81

Answer 60

In a report of 12 cats with lymphangiosarcoma, 9 presented with fast-growing, noncircumscribed subcutaneous masses and the others presented with a thoracic or abdominal mass. In all cats affected, the tumor was invasive and complete surgical resection was not possible.[72] In two additional cats with lymphangiosarcoma, one cat developed regional bony lysis in the affected limb and one cat developed immune-mediated hemolytic anemia.[73] Associated chylous effusions (pleural, abdominal, subcutaneous) have been reported.[74-76] Pulmonary lymphangiosarcoma was diagnosed in one dog presenting with a chylous effusion.[77] Diagnosis is confirmed by obtaining a biopsy specimen. Histologically, tumors of lymphatic endothelial origin are characterized by a neoplastic proliferation of endothelial cells. Immunocytochemical stains have been used to confirm the diagnosis in dogs and cats.[78-80] The identification of the factor VIII-related antigen and vimentin indicates the cells are of endothelial origin. The intensity and distribution of the stain has been used to attempt to differentiate lymphangiosarcomas from hemangiosarcomas but is often inaccurate. Newer specific markers to identify lymphatic endothelial cells have been identified in cats with lymphangiosarcoma.[79],[80] The prognosis with lymphangiosarcoma is poor with a high rate of local recurrence and metastasis. Most animals are euthanized or died due to severe lymphedema, pleural effusion, and/or distant metastases. There is one report with a positive response to mass resection and doxorubicin treatment. Recurrence of the mass or evidence of metastasis was not evident in a 9-month follow-up period.[81]